Nitrate Removal From Source Water In Biological Denitrification System Based On Agar As Carbon Source

Currently source water was polluted heavily by nitrate.A novel biological nitrate removal system was founded based on agar as the carbon source for nitrate removal from source water in biological denitrification system.Release property of organic matter from agar in deionized water and influences of running during biological denitrification in source water were research in batch experiments.Factors including rotating velocity, microbial biomass, initial DO, initial pH value, retention time, temperature, and agar/N mass ratio were studied in batch experiments;In continous systems, different HRTs,returning ratios, biomass, section water velocities and NO3--N concentrations were studied.The results showed that agar could be successfully used for carbon release, which was matched with power functions;microbial biomass,temperatures,C/N ratios,and retention times were of significant importance.The initial DO was of no significant impact on denitrification. When initial pH value was around 7.00, high NO3--N removal efficiency could be obtained. Influent NO3--N concentration had not so much effect on the NO3--N removal rate, and the retention time of 3 days and 7days were much better for nitrate influence concentration of 50.99mg/L and 102.49mg/L.At 25℃and 15℃,the optimized initial mass ratio of agar/NO3--N(g/g) for the highest NO3--N removal rate were 87.20:1 and 985.22:1.The highest nitrate removal rate can be 100% when biomass was 60.63nmolP/gAgar,rotating velocity was 120rpm,temperature was 25℃,nitrate influence concentration of 50.99mg/L and retention time was 3 days.The results of unit reactor showed that both column and tube reactors could be able to remove nitrate.The highest nitrogen removal rates were 51.02% and 81.34% in column and tube reactors respectively.The start of them needed about one month to stable running for nitrate removal.When HRT of column reactor was 6 hours, and HRT of tube reactor was 8 hours,influence nitrate concentration below 25mg/L,no returning and room temperature, the highest rate of them were 92.37% and 87.20%, respectively.The NO3--N removal rate increased with increasing of hydraulic retention time and decreasing of their cross-section velocities in tube and column reactor. When the influent NO3--N concentration was below 30mg/L and around 10mg/L, the maximum removal rate of 21.60% and 16% were obtained in reactor2.The average effluent NH4+-N concentration was 0.59mg/L.Organic matter and NH4+-N in BAF could be removed well when HRT=30min and gas/water ratio=1:1.The results of series system showed that nitrate removal rate was between 29% and 41% during the restart of agar-packed actor for about one month,and removal rate in column reactor was above 80% when the influent NO3--N concentration was around 55mg/L and HRT 12 hours. Effluent NO3--N concentration in reactor2, which failed to remove nitrate, was almost closed to 0. Reactor3,namely BAF, could reduce the effluent NH4+-N to the level between 0.02mg/L and 0.50mg/L,and corresponding CODMn between 0.30～7.80mg/L.The relationship of NO3--N removal rate(Y) and biomass(X) was Y=39.956X-0.2026.The series system of agar-based anoxic actor plus BAF could effectively reduce nitrate from drinking water when influent nitrate concentration below 30mg/L and HRT 6～8 hours.Water quality of system matched with the first standard of water quality standard for drinking water sources (CJ3020-93).The combined system is a promising biological denitrification treatment process with high efficiency and low cost.